Journal of Korean Endocrine Society 1994;10(2):98-104.
Published online November 6, 2019.
Evaluation of the Usefulness of Free T4 Measured by 2 - Step Iimmunoextraction in the Patients with Thyroid and Non - Thyroid Diseases.
Bo Youn Cho, Hong Kyu Lee, Jae Hoon Chung, Seok In Lee, Won Bae Kim, Chang Soon Koh
Many methods and commercial kits have become available for directly measuring free thyroxine(free T_4). However, most of them are inadequate for routine laboratory use because of their complexity and inaccuracy. Recently, 2-step RIA methods by immunoextraction(2-step immunoextraction) for free T_4 have been developed to improve its accuracy and convenience. We evaluated the usefulness of free T_4 measured by 2-step immunoextraction compared to free T_4 index(FT_4I), free T_4 measured by 1-step RIA, and TSH in 204 patients with thyroid and non-thyroid disease. There were no differences in sensitivities and specificities of free T_4(1-step, 2-step), FT_4I and TSH in the patients with hyperthyroidism and euthyroid nodule. However, the sensitivity of TSH in hypothyroidism was remarkablely higher than the others(100.0% vs. 61.5-81.5%). The sensitivity of free T_4(2-step) was also higher than those of free T_4(1-step), FT_4I and TSH in the patients with non-thyroid disease(94.3% vs. 74.3-83.8%). The values of free T_4 measured by 1-step RIA were significantly lower than those by 2-step immunoextraction, especially in the patients with non-thyroid disease(1.10+-0.04 vs. 1.55+-0.03ng/dL, p<0.05).In conclusion, no significant differences were found in sensitivity and specificity of free T_4(1-step, 2-step), FT_4I, and TSH in the patients with thyroid diseases except in hypothyroidism. However, the sensitivity of free T_4 measured by 2-step immunoextraction was significantly higher than the other tests, especially in the patients with non-thyroid disease. Therefore, free T_4 assay using 2-step immunoextraction is useful to differentiate the non-thyroid disease from thyroid diseases.
Key Words: Free thyroxine, 2 - step immunoextraction
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